5-Alkoxy 8 fluoro-1,2,4 triazolo[1,5 c]pyrimidine 2 sulfonamides (I), ##STR1## such as those described in EP 343,752 and U.S. Pat. No. 5,010,195, are valuable as herbicides. Compounds of this family are conveniently prepared from 2 alkylthio-4-hydrazino-5-fluoropyrimidines according to the following scheme. ##STR2##
2-Alkylthio-4-hydrazino 5-fluoropyrimidines are themselves conveniently prepared from 2,4 dichloro 5-fluoropyrimidine. Since the chloro substituent in the 4-position proves to be more reactive than that in the 2position, it is natural to first replace the chlorine in the 4 position with hydrazine and then to replace the chlorine in the 2-position with an alkyl mercaptan. ##STR3##
While this approach produces the desired 2-alkylthio -4-hydrazino-5-fluoropyrimidine, the yield is not exceptionally high. A similarly simple process that produces such hydrazinopyrimidines in good yield is thus highly desirable.